This invention relates to "moldless" tire retreading of the type where, in preparation for treatment within a heated pressure chamber, a rim-mounted tire having a replacement tread strip thereon is partially enclosed by a flexible impervious envelope having marginal edge portions that overlie opposite sidewalls of the tire and are sealingly engaged by respective ones of a pair of annular envelope-sealing members. The invention more specifically relates to an improved retreading apparatus by which the envelope-sealing members may be more efficiently, safely and precisely positioned and secured in association with tires of varying widths.